• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.4 s.175
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• pp.946-954
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• 2000

The purposes of the paper are to calculate stresses and strains of the disk with overcoating layer rotating quickly under normal loading and shear loading by contacting with head and to present material properties preventing the delamination between the disk and overcoating layer. The hard disk is modeled as two-layered disk composed with overcoating layer and the rest layers and the loading onto the disk is assumed axisymmetric. Solutions to equilibrium equations and compatibility equations are derived with the form of polynimial and Bessel function and coefficients satisfying boundary conditions are obtained differently for the case of body force, normal force and shear force. The risk of delamination are investigated for us to calculate the differences of strains at the interface between the disk and overcoating layer and the material properties preventing delamination are presented by calculating the differences of strains according to Young's modulus and density of disk.

• Earthquakes and Structures
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• v.7 no.5
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• pp.609-626
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• 2014

The capabilities of a high-resolution Digital Image Correlation (DIC) system are presented within the context of deformation measurements of full-scale concrete columns tested under reversed cyclic loading. The system was developed to have very high-resolution such that material strains on the order of the cracking stain of concrete could be measured on the surface of full-scale structural members. The high-resolution DIC system allows the measurement of a wide range of deformations and strains that could only be inferred or assumed previously. The DIC system is able to resolve the full profiles of member curvatures, rotations, plasticity spread, shear deformations, and bar-slip induced rotations. The system allows for automatic and objective measurement of crack widths and other damage indices that are indicative of cumulated damage and required repair time and cost. DIC damage measures contrast prevailing proxy damage indices based on member force-deformation data and subjective damage measures obtained using visual inspection. Data derived from high-resolution DIC systems is shown to be of great use in advancing the state of behavioral knowledge, calibrating behavioral and analytical models, and improving simulation accuracy.

• Geomechanics and Engineering
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• v.29 no.6
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• pp.615-626
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• 2022

The soft clays are widely distributed, and one of the prominent engineering problems is the creep behavior. In order to predict the creep deformation of soft clays in an easier and more acceptable way, a simple creep constitutive model has been proposed in this paper. Firstly, the triaxial creep test data indicated that, the strain-time (𝜀-t) curve showing in the 𝜀-lgt space can be divided into two lines with different slopes, and the time referring to the demarcation point is named as t_EOP. Thereafter, the strain increments occurred after the time t_EOP are totally assumed to be the creep components, and the elastic and plastic strains had occurred before t_EOP. A hyperbolic equation expressing the relationship between creep volumetric strain, stress and time is proposed, with several triaxial creep test data of soft clays verifying the applicability. Additionally, the creep flow law is suggested to be similar with the plastic flow law of the modified Cam-Clay model, and the proposed volumetric strain equation is used to deduced the scaling factor for creep strains. Therefore, a creep constitutive model is thereby established, and verified by successfully predicting the creep principal strains of triaxial specimens.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.6
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• pp.2284-2291
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• 2010

In this paper, we investigate the vibration analysis of plates, using an 8-node shell element that accounts for the transverse shear strains and rotary inertia. The forced vibration analysis of plates subjected to arbitrary loading is investigated. In order to overcome membrane and shear locking phenomena, the assumed natural strain method is used. To improve an 8-node shell element for forced vibration analysis, the new combination of sampling points for assumed natural strain method was applied. The refined first-order shear deformation theory based on Reissner-Mindlin theory which allows the shear deformation without shear correction factor and rotary inertia effect to be considered is adopted for development of 8-node assumed strain shell element. In order to validate the finite element numerical solutions, the reference solutions of plates are presented. Results of the present theory show good agreement with the reference solution. In addition the effect of damping is investigated on the forced vibration analysis of plates.

• Structural Engineering and Mechanics
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• v.68 no.5
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• pp.563-573
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• 2018

Temperature-induced responses, such as strains and displacements, are related to the boundary conditions. Therefore, it is required to determine the boundary conditions to establish a reliable bridge model for temperature-induced responses analysis. Particularly, bridge bearings usually present nonlinear behavior with an increase in load, and the nonlinear boundary conditions cause significant effect on temperature-induced responses. In this paper, the bridge nonlinear boundary conditions were simulated as bilinear translational or rotational springs, and the boundary parameters of the bilinear springs were identified based on the measured temperature-induced responses. First of all, the temperature-induced responses of a simply support beam with nonlinear translational and rotational springs subjected to various temperature loads were analyzed. The simulated temperature-induced strains and displacements were assumed as measured data. To identify the nonlinear translational and rotational boundary parameters of the bridge, the objective function based on the temperature-induced responses is then created, and the nonlinear boundary parameters were further identified by using the nonlinear least squares optimization algorithm. Then, a beam structure with nonlinear translational and rotational springs was simulated as a numerical example, and the nonlinear boundary parameters were identified based on the proposed method. The numerical results show that the proposed method can effectively identify the parameters of the nonlinear boundary conditions. Finally, the boundary parameters of a real arch bridge were identified based on the measured strain data and the proposed method. Since the bearings of the real bridge do not perform nonlinear behavior, only the linear boundary parameters of the bridge model were identified. Based on the bridge model and the identified boundary conditions, the temperature-induced strains were recalculated to compare with the measured strain data. The recalculated temperature-induced strains are in a good agreement with the real measured data.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.5
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• pp.493-504
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• 2008

This paper presents a computation of nonlinear elastic strains that may occur in the leaflet of the Edwards MIRA mechanical heart valve by the applied high blood pressure using the finite element analysis methodology. By adopting numerical analysis techniques of the commercial finite element analysis code, NISA, structural analyses of the Edwards MIRA mechanical heart valve are performed for the slight variation of leaflet thickness to get the elastic strains occurring in the leaflet while the high blood fluid pressures are applied to the leaflet surface in order that the maximum stress occurring in the leaflet may be less than the yield stress of the leaflet material(Si-Alloyed PyC). And so, only the geometric non-linearity is assumed because large geometric nonlinear elastic strains are expected rather than material nonlinear strains due to the applied high blood pressure. Computed linear and nonlinear elastic strains are compared to make sure the non-linearity of the computed elastic strain. The comparison result shows that large elastic strains occur clearly in the very thin leaflets as high blood pressures are applied. However, only the linear elastic strains occur for low blood pressures, and also for thick leaflets even for the high blood pressures. Hence the nonlinear structural analysis is very required in the structural design of a mechanical heart valve.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.95-100
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• 2008

A 4-node assumed strain finite element based on higher order shear deformation theory is developed to investigate the behaviours of symmetric and unsymmetric laminated composite plates. The present element is based on Reddy's higher order shear deformation theory so that it can consider the parabolic distribution of shear deformation through plate thickness direction. In particular, assumed strain method is adopted to alleviate the shear locking phenomena inherited plate elements based on higher order shear deformation theory. The present finite element has seven degrees of freedom per node and denoted as HSA4. Numerical examples are carried out for symmetric and unsymmetric laminated composite plate with various thickness values. Numerical results are compared with reference solutions produced by other higher order shear deformation theories.

• Korean Journal of Medicinal Crop Science
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• v.25 no.2
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• pp.108-114
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• 2017

Background: The study was conducted to investigate the distributions of faecal bacteria in commercial oriental medicine herb products. Methods and Results: A survey was conducted on the microbial contamination levels and antimicrobial specificity of Bacillus cereus and other microbes using 106 oriental medicine herb products on sale in Seoul. Pouring and isolation methods such as standard plate counts were used to identify the bacteria. The isolated bacterias included coliforms, Bacillus spp., Enterococcus spp., Staphylococcus spp., Listeria spp.were identified by using gram staining and an API (analytical profile index) kit. Antimicrobial drugs discs were determined by CLSI (clinical and laboratory standards institute). Conclusions: The bacterial isolates present in the herbal medicines included 98 coliforms, 45 Bacillus spp., 29 Enterococcus spp., and 2 Listeria spp. Among these, there were nine Bacillus cereus strains, one Enterococcus faecium strain, and one Enterococcus faecalis strain present. The 9 Bacillus cereus strains were tested for susceptibility to 36 types of antibiotics products by the disc diffusion method. The strains showed resistance to 13 of these antibiotic products and semi-resistance to 5 antibiotic products. On the basis of these results, any oriental medicine herb product can be assumed to be contain resistant or semi-resistant bacterial strains. Therefore, we suggest prescribing guidelines and special management for the use of antibiotics in farms producing oriental medicine herb products.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.2
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• pp.1-10
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• 2012

In the present study, an Element-Based Lagrangian Formulation for the nonlinear analysis of shell structures is presented. The strains, stresses and constitutive equations based on the natural co-ordinate have been used throughout the Element-Based Lagrangian Formulation of the present shell element which offers an advantage of easy implementation compared with the traditional Lagrangian Formulation. The Element-Based Lagrangian Formulation of a 9-node resultant-stress shell element is presented for the anisotropic composite material. The element is free of both membrane and shear locking behavior by using the assumed natural strain method such that the element performs very well in thin shell problems. The arc-length control method is used to trace complex equilibrium paths in thin shell applications. Numerical examples for laminated composite curved shells presented herein clearly show the validity of the present approach and the accuracy of the developed shell element.

• Structural Engineering and Mechanics
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• v.18 no.6
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• pp.807-829
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• 2004

The Element-Based Lagrangian Formulation of a 9-node resultant-stress shell element is presented for the isotropic and anisotropic composite material. The effect of the coupling term between the bending strain and displacement has been investigated in the warping problem. The strains, stresses and constitutive equations based on the natural co-ordinate have been used throughout the Element-Based Lagrangian Formulation of the present shell element which offers an advantage of easy implementation compared with the traditional Lagrangian Formulation. The element is free of both membrane and shear locking behavior by using the assumed natural strain method such that the element performs very well in thin shell problems. In composite plates and shells, the transverse shear stiffness is defined by an equilibrium approach instead of using the shear correction factor. The arc-length control method is used to trace complex equilibrium paths in thin shell applications. Several numerical analyses are presented and discussed in order to investigate the capabilities of the present shell element. The results showed very good agreement compared with well-established formulations in the literature.